Interlock switch mechanisms



2 Sheets-Sheet l A. C. FIELDS ETAL INTERLOCK SWITCH MECHANISMS Nov. 29, 1955 Filed May 4, 195s lll lll' Nov. 29, 1955 A. c. FIELDS ETAL 2,725,437

INTERLOCK SWITCH MEcHANIsMs Filed May 4, 1953 2 Shee'cs-SheekI 2 United States Patent 2,125,437 y INTERLocK SWITCH MEcHANrsMs Application May 4, 1953, Serial No. 352,672

Claims. (Cl. 20G-61.67)

This invention relates to interlock switch mechanisms such as are used with doors providing access to equipment charged to high voltages. v

In electrostatic precipitators, itis customary tokemploy screw operated interlock switches with doors which provide access to the high voltage components of the power supply packs of the precipitators. After such a screw has been unscrewed a few turns an associated switch is opened for disabling the power pack. The screw must be completely unscrewed before the 'associated-doorcan be opened, and the time required for completely unscrewing the screw after the switch has opened, provides an interval suicient for the high voltage stored in the capacitance of the power pack to become dissipated.

An irksome disadvantage of such a device is that the same long time is required to insert the screw and to close the switch as is required to remove the screw. A protective time interval is neither required or desired in closing the interlock switch.

This invention provides a screw actuated interlock switch mechanism in which the actuating screw is simply pushed into position for closing the switch, but which must be unscrewed for opening the switch and the associated access door.

In one embodiment of this invention, an actuating screw is litted in a tube having a slot extending from its surface at one side to the screw, at an acute angle to the longitudinal axis of the tube. A spring biased member fitted in the slot rides over the threads on the screw when the latter is pushed inwardly, providing for quick insertion of the screw. Upon withdrawal of the screw, the spring biased member engages the threads on the screw requiring the screw to be rotated and unthreaded from the spring biased member.

An object of this invention is to provide an interlock switch mechanism with an actuating screw which can be quickly inserted but must be slowly removed.

Another object of this invention is to provide a power pack with an access door and a disabling switch, both of which can be quickly closed but cannot be quickly opened.

This invention will now be described with reference to the drawings, of which:

Fig. 1 is a plan view partially in section, and with a portion of its upper side removed, of an interlock switch mechanism embodying this invention, in place upon one wall of a power pack, with the switch and the access door of the power pack in closed positions;

Fig. 2 is a side elevation, partially in section and with a portion of its front side removed, of the switch assembly of Fig. 1;

Fig. 3 is a view similar to Fig. 2 but with the actuating screw shown far enough unscrewed to have opened the switch, and

Fig. 4 is a sectional view along the lines 4-4 of Fig. 3.

An access door to high voltage equipment, in closed position rests in alignment with a cooperating wall 11.

ICS

The door 10 has a metal strap 13 held thereto by the screws 14, and which has a central circular opening through which the rivet 15 fastened to the strap extends. The rivet 15 has a cylindrical stem portion 16 slidably fitted in the slot 17 in the bracket 18.

The bracket 18 has an end portion 19 extending perpendicular to the bracket portion containing the slot 17, and which contains a circular opening 20 for the reception of the actuating screw 21 of the interlock switch assembly. The stem 22 of the screw 21 has the collar 23 secured thereto and which is larger than the opening 20, and which is provided for retaining with the head of the screw 21, the screw 21 to the bracket when the screw 21 is removed from the switch assembly as will be described later.

The screw 21 has a threaded portion 24 which extends through a circular opening in the inner side plate 25 of the interlock switch box 26. The plate 25 has a tube 27 extending inwardly of the box 26, and through which the threaded portion 24 of the screw 21 extends.

An electric switch 28 is bolted to the flange 29 Within the box 26, and has a spring arm 30 which is moved downwardly by the inner end of the screw 21 when the latter is in its innermost position as illustrated by Figs. l and 2 of the drawings, so that it pushes the plunger 31 downwardly for closing the switch contacts.

The tube 27 has a slot 32 in one side thereof, extending at an acute angle to the longitudinal axis of the tube, with the sides of the angle converging towards the plate 25. The spring 33 has a portion 34 extending through the slot 32, and has a portion 35 wrapped around the portion of the tube 27 opposite the slot 32 and then crossing the portion 34. This biases the spring portion 34 downwardly against the threaded portion 24 of the screw 21.

The spring portion 34 ts in between adjacent threads of the screw 21. When the screw 21 is pushed inwardly, the spring portion 34 moves outwardly in the slot 32 permitting the threads of the screw 21 to pass freely under the spring portion 34 so the screw 21 can be quickly pushed inwardly.

The screw 21 cannot, however, be freely moved outwardly since any outward movement of it causes the spring portion 34 to iit in between adjacent threads of the screw 21 and to act as a nut and requiring the screw 21 to be rotated in the proper direction to unthread it from the spring portion 34.

When the screw 21 is in its innermost position as illustrated by Figs. 1 and 2 of the drawings, the switch 28 is closed, and the access door 10 is locked by the screw 2l extending through the bracket wall 19.

As the screw 21 is unscrewed from its innermost position and thereby moved outwardly, its collar 23 by contacting the bracket wall 19 causes the bracket 18 to slide outwardly through the movement of its slot 17 past the rivet 15. When the bracket 18 has been moved outwardly by the outward movement of the screw 21 to its outermost position, the inner end of the screw 21 will have cleared the plate 25 of the box 26 so that the door 10 can be opened.

When the screw 21 has been unscrewed to an intermediate position as illustrated by Fig. 3 of the drawings, its inner end will have cleared the spring arm 30 or the switch, permitting the spring arm 30 to move upwardly to clear the switch plunger 31 permitting the latter to move upwardly under the usual spring bias and to open the switch contacts, thereby deenergizing the power pack for which the interlock switch is provided. The lter capacitance of the power pack would remain charged when the switch was opened, but by the time the screw 21 has been unscrewed suiiiciently outwardly to permit the access door 10 to be opened, the charge will have leaked off through the usual bleeder resistors.

After the purpose for which the access door 10 has been opened, is completed, following the closing of the door, the screw 21 is simply pushed inwardly within the box 26 to its innermost position. The switch 28 is then closed and the door 10 is then locked.

What is claimed, is:

1. An interlock switch assembly comprising a tube, a switch closing member opposite one end of said tube, a screw insertable in said tube from the other end thereof for actuating said member, said tube having a slot therein extending at an angle to the longitudinal axis of said tube, and means in said slot and spring biased against the threads of said screw and requiring rotation of said screw for moving said screw in a direction away from said member and riding over said threads when said screw is pushed towards said member.

2. An interlock switch comprising a tube, a switch closing member opposite one end of said tube, a screw insertable in said tube from the other end thereof for actuating said member, said tube having a slot therein which extends from the exterior thereof into said tube, the plane of the slot extending at an acute angle to the longitudinal axis of said tube, the apex of said angle being nearest said other end of said tube, and means in said slot spring biased against the threads of said screw and requiring rotation of said screw for moving said screw in a direction away from said member and riding over said threads and moving outwardly in said slot when said screw is moved towards said member.

3. An interlock switch assembly as claimed in claim 1 in which a door locking member is provided opposite said other end of said tube, and in which said screw extends through said door locking member and said tube against said switch closing member when said switch closing member is in switch closing position.

4. An interlock switch as claimed in claim 2 in which a door locking member is provided opposite said other end of said tube, and in which said screw extends through said door locking member and said tube against said switch closing member when said switch closing member is in switch closing position.

5. An interlock switch assembly comprising a tube, a switch closing member opposite one end of said tube, a screw insertable in said tube from the other end thereof for actuating said member, said tube having a slot therein between said ends which extends from the exterior of said tube into said tube, the plane of said slot extending at an acute angle to the longitudinal axis of said tube, the apex of said angle being nearest said other end of said tube, means in said slot spring biased against the threads of said screw and requiring rotation of said screw for moving said screw in a direction away from said member and riding over said threads and moving outwardly in said slot when said screw is moved towards said member, a bracket around said screw opposite said other end of said tube, said bracket having a slotted portion extending parallel to said screw, and a guide member for attachment to a door in the slot of said slotted portion of said bracket.

No references cited. 

